Author Topic: Broken Yamaha RX-A700  (Read 3247 times)

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Offline mzacharias

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Re: Broken Yamaha RX-A700
« Reply #25 on: April 29, 2019, 12:13:01 am »
so the NPN output transistors have 22 volts on the collector and 7 volts on the base and the emitter. the PNP side has .5 volts on the collector and still the 7 volts on the others. So is this the offset you were referring to? cause it's an offset but i'm not sure what would cause this and yes it is all of the NPNs that have the 22 on the collector. Thanks for your help!

Yes, this is a DC offset. It's important to determine whether it exists on all channels, or just one. If on all channels, once again look to power supply issues.

Turn the receiver ON and let it shut off again by it's protection function. Then turn on in diagnostic mode and be prepared to make note of the initial display, like PS PRT 022L of something like that. This will tell us which way to go.
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #26 on: April 29, 2019, 12:57:12 am »
I think I have been on a wild goose chase with the amplifier circuit... after a lot of head banging I think I have ruled it out as fine... I think. So I guess time to look at the protection circuit then.
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #27 on: April 30, 2019, 01:31:14 am »
So I started on the second receiver and it just needed to be started in the diagnostic mode and it cleared up and works. the other however has a ps2 prt:182 H so I have looked into this and I see that you have seen this exact code on another post. I have replaced the 5v regulator and I have the same code so then I up and replaced the top two of the three stacked boards to see if the problem went with it and it did no so its on the operations board or the bottom amplifier board.
 

Offline Satbeginner

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Re: Broken Yamaha RX-A700
« Reply #28 on: April 30, 2019, 07:31:30 am »
Hi,

I had something similar, one of the tests showed a voltage out of range (don't remember which) , I had to replace a TO-220 12V regulator all the way on the left at the internal heatsink, playing great ever since..

Un saludo,

Leo
You need a scope to repair a scope, and you need many multimeters to repair another multimeter!
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Offline mzacharias

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Re: Broken Yamaha RX-A700
« Reply #29 on: April 30, 2019, 01:50:54 pm »
So I started on the second receiver and it just needed to be started in the diagnostic mode and it cleared up and works. the other however has a ps2 prt:182 H so I have looked into this and I see that you have seen this exact code on another post. I have replaced the 5v regulator and I have the same code so then I up and replaced the top two of the three stacked boards to see if the problem went with it and it did no so its on the operations board or the bottom amplifier board.

I think if the protection value is HIGH, there may be a missing negative voltage, like a -12V or the like.
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #30 on: April 30, 2019, 11:24:27 pm »
well I was working on the second receiver, it worked then I was swapping parts with each other. this swapping required soldering and I was way to tired and didn't check for solder bridges and so I shorted 3 ac lines and let out some magic smoke. I then fixed the bridges and found that the transformer was still good. however the receiver then output the same ps2 prt code so I have been checking stuff in the power supplies. the ps2 prt line should be 1.2 volts but it's 5 volts. I was doing something dumb by directly powering the transformer with an auto transformer and then bang on of the output transformers blew a chunk out of its face. so once I fix this channel I need to fix the other problem... any thoughts?
 

Offline mzacharias

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Re: Broken Yamaha RX-A700
« Reply #31 on: May 01, 2019, 01:33:16 pm »
well I was working on the second receiver, it worked then I was swapping parts with each other. this swapping required soldering and I was way to tired and didn't check for solder bridges and so I shorted 3 ac lines and let out some magic smoke. I then fixed the bridges and found that the transformer was still good. however the receiver then output the same ps2 prt code so I have been checking stuff in the power supplies. the ps2 prt line should be 1.2 volts but it's 5 volts. I was doing something dumb by directly powering the transformer with an auto transformer and then bang on of the output transformers blew a chunk out of its face. so once I fix this channel I need to fix the other problem... any thoughts?

Put it in Protection Cancel mode and look at all the power supply voltages, and if you have it apart, make sure all the grounds are qualified (connected).
 

Offline plurn

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Re: Broken Yamaha RX-A700
« Reply #32 on: May 10, 2019, 05:41:55 pm »
same problem/fix as these maybe? it is a common issue with some Yamaha receivers:

"replace capacitor C405 (the red one on this video) : 22nF/630V"
Yamaha receiver NO POWER : FIX (all models)
https://youtu.be/JTeq07wL2aU?t=1

EEVBlog #379 - Yamaha RX-V557 Receiver Fix
https://youtu.be/MwvjAtSr5t8?t=1
« Last Edit: May 10, 2019, 06:07:24 pm by plurn »
 

Offline mzacharias

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Re: Broken Yamaha RX-A700
« Reply #33 on: May 11, 2019, 02:15:30 am »
so the NPN output transistors have 22 volts on the collector and 7 volts on the base and the emitter. the PNP side has .5 volts on the collector and still the 7 volts on the others. So is this the offset you were referring to? cause it's an offset but i'm not sure what would cause this and yes it is all of the NPNs that have the 22 on the collector. Thanks for your help!

7 volts on the emitters is easily enough to put the receiver into protect mode. If it's all the channels, like you say, there's a voltage missing. I'll glance at the schematic and either re-post or edit this post.

edit: OK, look at the output of Q1072, a 2SA1708. Should be about -12.6 volts. I'm betting this voltage is missing. It can be measured at the - side of capacitor C1075, since the transistor legs are flush to the board.
« Last Edit: May 11, 2019, 02:20:20 am by mzacharias »
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #34 on: May 13, 2019, 03:22:59 am »
I'll have to check on that, I stopped working on them because I got a  little frustrated because I blew the transistor out, but I will have to check that power rail. thanks
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #35 on: May 13, 2019, 10:30:16 pm »
so, I have been looking at the power rails, and it looks like the +12 and -12 are shorted together and when they are powered they equally get 29 volts so thats an issue
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #36 on: May 13, 2019, 10:32:40 pm »
maybe I was wrong, this is confusing
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #37 on: May 13, 2019, 10:57:43 pm »
the 12 and -12 are fine, I had meen measuring it in the incorrect spot
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #38 on: May 17, 2019, 12:09:03 am »
So after a while of poking around I have found that IGND is around 1.5 volts... and it should be 0. So I think there is a problem on the operation(2) board unless someone thinks its else where. What do you people think about it? any suggestions? thanks
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #39 on: May 17, 2019, 12:44:49 am »
as well, on the +12 and -12 v lines its 2v on 12 and -22 on the -12 and my ground point is the E line on the board. I dont know why this is but it is so there you go
 

Offline mzacharias

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Re: Broken Yamaha RX-A700
« Reply #40 on: May 17, 2019, 04:47:02 pm »
Does seem based on what you said that you have a ground floating.

Are all the rear panel screws in place?
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #41 on: May 19, 2019, 02:21:24 am »
no but I have alligator clips connecting everything and it is still the same
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #42 on: May 20, 2019, 11:48:39 pm »
I have found that there are some points on the pcbs where the E which should be 0v it is -7.5v. The other voltages around which are +18 +12 and -12 are all reduced by -7.5v
 

Offline bob91343

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Re: Broken Yamaha RX-A700
« Reply #43 on: May 21, 2019, 12:18:34 am »
Yup, missing ground.
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #44 on: May 21, 2019, 08:33:22 pm »
But I'm pretty sure it's not tho everything is grounded with alligator leads
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #45 on: May 21, 2019, 08:34:22 pm »
Missing ground would make sense but i have connected all the ground planes
 

Offline mzacharias

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Re: Broken Yamaha RX-A700
« Reply #46 on: May 21, 2019, 09:09:59 pm »
I would confirm good continuity between the center point of the two main filter caps, the rear panel, the outer jackets of the RCA connectors, and the main heat sink.
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #47 on: May 21, 2019, 09:54:32 pm »
I didn't have the power button connected and that was the problem for the offset but the Ignd is 5 volts now and the ps2-prt is 2.5v when it should be around 1.2
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #48 on: May 21, 2019, 09:57:32 pm »
it wasnt the power button it was the headphone jack
 

Offline CoopedUp

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Re: Broken Yamaha RX-A700
« Reply #49 on: May 25, 2019, 09:08:07 pm »
I still can't seem to find the problem with these guys... It's a wild goose chase
 


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